The principal problems that occur during the extraction and transportation of crude oil is the foam formation, due to the presence of gas. In general, the greater tendency to foaming and foam collapse occurs in crude oils with lower density to 40 degrees API. Foaming phenomena, substantially, cause operational problems such as: low productivity, pump cavitation (Fallin et al, 1971), deposit formation, liquid sweeping into the gas streams, water and gas sweeping into the crude oils streams and reduction of the separator capacity (Wylde et al, 2008). Depending on the nature of the crude oil and the type of separators used, the problems of foaming (sweeping of liquid in gas streams and entrance of gas into flows of fluid) can reduce the crude oil production and even cause unexpected shutdowns of the process. The problems result in equipment and containers inundations, but also these situations can cause reductions in the capacity of crude oil and gas separators. (Poindexter et al, 2002).
An antifoaming agent is a chemical substance with surfactant properties (change in the surface tension) which when present in a solution facilitates the foam removal. The antifoaming agent must be insoluble in the crude oil, causing sudden gradients in the oil-gas surface tension, should not be sensitive to changes in temperature, and must be resistant to chemical and oxidative attack. (R. Prud'homme et al, 1996). Crude oil or petroleum (literally means “rock oil”) is a mixture of hydrocarbon compounds, gases and liquids. Usually crude oil is liquid, is contained in deposits of sedimentary rocks and may also contain small amounts of sulfur compounds, nitrogen, oxygen and metal traces. (Speight J., 2001).
Foam formation inhibition in crude oils is a highly complex multifactorial problem. The literature reports that an efficient antifoam agent needs to penetrate the gas/crude oil interface and to disperse it over the crude oil surface. (Blute et al, 1994). Among commercially products used as antifoaming agents for crude oils can be mentioned the following: silicones and fluorosilicones, phosphate esters, metallic fatty acid surfactants, sulfonated compounds, amides, polyglycols, glycolic esters, polyethers, esters of fatty acids and alcohols (Prod'homme et al, 1996). Among the most used are silicone based products because of their high antifoaming ability, due to the fact that these chemicals are effective at low concentrations around 10 ppm or less. However, silicon based antifoaming agents in large amounts present problems such as catalysts poisoning in refining processes and the formation of deposits in other subsequent steps.
Traditionally, silicone (dimethyl polysiloxane) was used for the treatment of foam inhibition. In U.S. Pat. No. 2,702,793, a mixture of dimethyl silicone and amyltriethoxysilane is used for inhibiting foam formation in crude oils. Similarly, U.S. Pat. No. 2,862,885 describes the use of monovinylalkoxysilane as antifoaming agent in crude oil. In contrast, U.S. Pat. No. 4,005,044 discloses the use of a dimethylpolysiloxane liquid as an antifoaming agent in a solution of emulsifying agent.
In order to improve the performance of the polysiloxanes as antifoaming agents, chemical modifications have been made to these polymers. Chemical modification is to obtain copolymers such as the linear copolymer fluoro-alkyl polysiloxane, as disclosed in U.S. Pat. No. 4,329,528, with a composition between 20-70% mol of fluorosilicone, presenting a great performance at high temperatures (in the range from 25 to 370° C.) and good solubility in crude oil. This copolymer is used in crude reserves as a method to inhibit or suppress foam formation, adding at least 1 ppm of the antifoaming agent (Evans, 1982).
WO 97/38067 and U.S. Pat. No. 6,001,140 describes the use of copolymers, which have a base structure consisting of polysiloxane and to which is grafted an organic group, particularly a polymer with the formula MDxD′yD″zM where M is O0.5Si (CH3)3, D is a OSi(CH3)2, D′ is OSi(CH3)R and D″ is OSi(CH3)R′. At the same time, R is a polyhydric organic group, C6-C28, while R′ is a phenol derivative or a long chain aliphatic group.
Cassani F. et al. presented laboratory and field studies in the evaluation of six commercial silicon based antifoaming agents in medium density crude oils (21 to 27° API), and the optimal doses for controlling the foam generated in the separation equipment. The optimal dosages for these silicon based antifoaming agents (formulation containing between 2 and 4% of silicon in kerosene as solvent) in a medium crude oil of 26.3° API, were found to be in a range from 0.01 to 1 ppm in laboratory tests. These doses were corroborated at field level.
Due to operational difficulties involved with the use of silicon based products, some have sought new alternatives of free-silicon compounds, to evaluate them as antifoaming agents in crude oil. Those antifoaming agents called “free-silicon” are organic compounds consisting essentially of sulphates and phosphates (Hart, 1992), vegetable oils (Hart, 1994) and animal oils (Hart, 1995), compounds of polyisobutylene (Hart, 1995 and Hart, 1998), block copolymers of polypropylene oxide/polyethylene oxide (Hart, 1998) and mixtures thereof.
Vegetable oils such as jojoba oil (Simmondsia chinensis) and animal oils such as mink oil (Neovison vison) have been used to control foam at high temperatures (150 to 500° C.) in hydrocarbon fluids, during the distillation and/or delayed coking crude oil processes, as indicated in U.S. Pat. No. 5,296,132 and U.S. Pat. No. 5,389,299, respectively. Effective doses like antifoaming agents in the patents cited ranged from 10 to 1000 ppm (Hart, 1994, 1995) and given the low viscosity of these products may be added in pure form or in solution.
U.S. Pat. No. 5,472,637 and U.S. Pat. No. 5,800,738 describe the use of polyisobutylene of high molecular weight (between 2000 and 2 000 000 Daltons) and low molecular weight (320), being effective as antifoaming agents in crude oil and/or in its derivatives.
Alkoxylated alkylphenol/formaldehyde block copolymer compounds of propylene oxide/ethylene oxide, with molecular weights between 2000 to 6000 Daltons were developed for foaming control in separation systems of hydrocarbons hydrocracking in doses from 15 to 1500 ppm as disclosed in U.S. Pat. No. 5,750,052.
Drilling or well treatment methods have been developed that prevent the formation or breaking of foam, treated fluid is a liquid that is added with an anti-foaming agent. The antifoaming agent composition may be useful in the preparation of the well (drilling fluids, fluid foundation, etc.). This simple addition prevents foaming and air swept during stirring, mixing or pumping fluids like them. The composition of these antifoaming agents comprises a carboxylic acid amide, a propylene glycol, and a fatty alcohol (C12-15) ethoxylated and propoxylated (Chatterji, 2007, 2009, 2011).
Rezende D. A., et al. evaluated the efficiency of commercial antifoaming agents, such as poly (ethylene oxide) poly (propylene oxide) block copolymer and polyether grafted polysiloxanes in two crude oil samples with SARA compositions (analysis of saturates, aromatics, resins and asphaltenes), like as well as its density and viscosity, (Danielle, 2011). Polysiloxanes grafted with polyether like pendant groups showed the best performance as foam inhibitors in crude oil.
Wylde J. has studied foaming in crude oils from northern Alberta, Canada, with densities of 10 to 12° API. However, using the evaluation method for foaming described in their study (modified from the ASTM D892-13 standard method) and due to the high viscosity of super-heavy crude oil selected to evaluate (12° API), it was not feasible to create significant levels of foam to perform evaluations of the antifoaming agents under study. To overcome this difficulty, a substantial amount of n-heptane was added to the super-heavy crude oil in order to create an artificial light crude oil of lower viscosity and thus be able to measure the foam inhibitory efficiency from antifoaming agents. Clearly, the addition of n-heptane leads to loss of the asphaltenes in the crude oil. Antifoaming agents studied were all free-silicon chemical compounds: compounds based on sulfates and phosphates, ethoxylated esters, polyethylene glycol esters, ethoxylated alcohols (11 commercial chemical products obtained from the market). Field tests were shown to be effective as antifoaming agents mixtures of sulfonated salts and ethoxylated fatty alcohol adducts of ethylene oxide and propylene oxide. One limitation of this study is that the above chemicals are only effective as antifoaming agents in deasphalting crude oil and not in real heavy crude oils.
As regards on polyacrylates or acrylic, there are several references to its application in the conditioning of petroleum and its derivatives. Its capacity has been reported as antifoaming agents in oil derivatives from petroleum, such as: lubricating oils for internal combustion engines, pumps lubricant oils, hydraulic oils, etc. These lubricants may be synthetic or natural, as described in U.S. Pat. No. 3,166,508. The major efficiency of polyacrylates as antifoaming agents in petroleum derivative lubricating oils is observed at concentrations of 10 to 50 ppm. However, polyacrylates disclosed in this patent have the disadvantage of being effective only in certain types of oil. The patent to which it is referenced do not make mention of the application of polyacrylates as antifoaming agents in any crude oil conditioning process. This patent does not disclose adjusting the molecular weight of the polyacrylates in order to increase their efficiency as antifoaming agents in specific samples of crude oil. U.S. Pat. No. 5,766,513 describes a combination of a fluorosilicone base antifoaming agent with one based on polyacrylate which is effective to reduce the foam in lubricant oils at low and high. However, by themselves, none is efficient in reducing foam at evaluation conditions. In the other hand, it has been reported that acrylates copolymers and terpolymers (mainly from alkyl methacrylate type monomers, wherein the alkyl moiety contains a fluoroaliphatic group of 3 to 20 carbon atoms) have shown to increase the resistance to foaming once they are added to hydrocarbon lubricant oils. The copolymers and terpolymers based on acrylates are disclosed in U.S. Pat. No. 7,700,527 and EP 1029030, respectively.
Among other applications of the polyacrylates for petroleum conditioning, different to the inhibition of the formation of foams, their use as pour point depressor in crude oils with high content in paraffinic waxes as disclosed in U.S. Pat. No. 3,951,929. Acrylics also have shown high performance as viscosity reducers in heavy crude oils, such as described in U.S. Patent Publication No. 2011/0067295 (Castro, 2011).